Article pubs.acs.org/est
Minimizing the Energy Requirement of Dewatering Scenedesmus sp. by Microfiltration: Performance, Costs, and Feasibility Michael L. Gerardo,* Darren L. Oatley-Radcliffe, and Robert W. Lovitt Centre for Complex Fluids Processing, Multidisciplinary Nanotechnology Centre, College of Engineering, Swansea University, Swansea SA2 8PP, United Kingdom S Supporting Information *
ABSTRACT: The harvesting of the microalgae Scenedesmus species using a 200 L pilot-scale microfiltration system was investigated and critically assessed. The energy requirement was determined and correlated to the different operating parameters, such as transmembrane pressure (ΔP), membrane area, temperature, and initial biomass concentration. A filtration model was developed and showed a strong correlation with experimental data up to 20.0 g of dry cell weight (DCW)/L. The non-optimized filtration system had an energy requirement of 2.23 kWh/m3 with an associated cost of $0.282/kg of microalgae. The investigation into the influence of the operating parameters and scale-up effects showed that the energy requirement could be substantially reduced to 0.90 kWh/m3 and $0.058/kg of microalgae harvested. Maintenance costs associated with cleaning were estimated to be 0.23 kWh or $0.029/batch of microalgae processed. Dependent upon the operating conditions, harvesting may represent 6−45% of the energy embedded in the microalgae with a carbon footprint of 0.74−1.67 kg of CO2/kg of microalgae. Microfiltration was demonstrated to be a feasible microalgae harvesting technology allowing for more than 99% volume reduction. The energy requirement and associated carbon footprint of microalgae harvesting reported here do not forfeit the need for an industrial-scale study; however, the information provided presents a more realistic approximation than the literature reported to date.
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INTRODUCTION In 2009, the European Commission Renewable Energy directive set out a target to achieve 10% renewable energy in the transport sector by 2020. However, a subsequent critical evaluation of land usage when assessing the greenhouse performance of biofuels and bioliquids led to a change in this target to 5% in 2012. This ignited an interest in alternative feedstocks for biodiesel, which do not rely on arable land. As a direct consequence, microalgae have become the center of much attention from the scientific community.1−3 Cultivated in photobioreactors, such as ponds, tubes, and tanks, microalgae grow at very dilute concentrations (
